Various aluminate phosphors have been put to practical use as phosphors for energy-saving fluorescent lamps. As a blue phosphor, for example, (Ba,Sr)MgAl10O17:Eu (BAM:Eu) is mentioned. As a green phosphor, for example, CeMgAl11O19:Tb, BaMgAl10O17:Eu,Mn, and the like are mentioned.
In recent years, BAM:Eu, which has high luminance under vacuum-ultraviolet excitation, has been used as a blue phosphor for a PDP.
However, when a light-emitting device using the blue phosphor BAM:Eu is driven for a long period, the luminance is degraded significantly. Hence, in the light-emitting device use, particularly in the PDP use, there is a strong demand for a phosphor that shows less luminance degradation even after the long-time driving.
On the other hand, methods using certain types of silicate phosphors for a light-emitting device are proposed. For example, JP 2003-132803 A and JP 2004-176010 A disclose methods using (Sr1-a, Baa)3-dMgSi2O8:Eud (where 0≦a≦1, 0.01≦d≦0.1). JP 2006-12770 A discloses a method using M3-eMgSi2O8:Eue (where M is at least one element selected from the group consisting of Sr, Ca and Ba, and 0.001≦e≦0.2). JP 2006-124644 A discloses a method using 3M1O.mMgO.nSiO2 (where M1 is at least one element selected from the group consisting of Sr, Ca, and Ba, and 1≦m≦1.5, 2≦n≦2.6, 3<m+n).
According to elaborate studies of the present inventors, however, it has been found that in most cases in the light-emitting devices using the above conventional phosphors, the phosphors can not inhibit the degradation of luminance during driving while maintaining the high luminance. In addition, when a phosphor in which a Sr site is not replaced with Ba is used, the phosphor has higher chromaticity y and worse color purity than those of the blue phosphor BAM:Eu used in the current PDP. On the other hand, when a phosphor in which a Sr site is replaced with Ba is used, the luminance intensity of the phosphor drops significantly. Furthermore, when the above conventional phosphor having a Sr site is used, the degradation of luminance is significant during the manufacturing processes of applying and firing the phosphor with an organic binder. These constitute problems.